Fouling is the progressive loss of membrane performance from material depositing on or in the membrane. Identifying which of the four fouling types dominates is the key to the right pre-treatment.
Suspended and colloidal solids cake the membrane; controlled by SDI/MFI and upstream clarification and filtration.
Sparingly soluble salts precipitate as recovery concentrates the feed; controlled by antiscalant and recovery limits.
Natural organic matter adsorbs and microorganisms form biofilm; the most persistent and the hardest to reverse.
The Silt Density and Modified Fouling Indices quantify particulate and colloidal fouling potential of the feed.
LSI and S&DSI predict carbonate and sulphate scaling risk along the array.
Assimilable organic carbon and ATP indicate the feed's tendency to support biofilm.
Membrane suppliers tie warranties to feed quality, commonly SDI15 < 3 to 5 and turbidity < 0.5 NTU, because particulate and colloidal fouling is largely irreversible. The Silt Density Index measures the rate at which a 0.45 µm filter blocks under standard conditions, while the Modified Fouling Index reflects the cake-filtration mechanism more directly. These indices set the duty of the DAF, media or UF pre-treatment, and are the routine field check that the pre-treatment is protecting the membranes.
DAF, media and UF pre-treatment cut SDI and turbidity to protect the membrane.
Antiscalant dosing and recovery limits manage sparingly soluble salts.
Source control, biocide strategy and CIP manage biofilm.
Reynolds & Bauhm designs membrane systems and the pre-treatment that protects them — from UF/MF and SDI control to RO array design, energy recovery and CIP.
Our expertise spans multiple industries with sector-specific water treatment solutions.